An epitaxial growth technique, which grows a monocrystalline thin film of a compound semiconductor such as GaN and SiC on a monocrystalline substrate such as a sapphire substrate, a GaN substrate, a SiC substrate, and a silicon substrate, is used to produce an electronic device such as a light emitting diode (LED) and a power semiconductor.
A wafer is placed inside a film formation chamber kept at a normal pressure or a reduced pressure in a film formation apparatus used in the epitaxial growth technique. Then, when a gas as a material for film formation is supplied into the film formation chamber while the wafer is heated, a pyrolysis reaction and a hydrogen reduction reaction of a material gas occur on the surface of the wafer, thereby forming an epitaxial film on the wafer.
It is necessary to accurately control the temperature of the wafer in order to deposit a high-quality film with uniform thickness and quality on the wafer. For this reason, the temperature of the wafer is measured using a radiation thermometer and the output of a heater is controlled (for example, see Patent Literature 1).
The radiation thermometer measures the temperature of an object by measuring the strength of infrared light and visible light which is radiated from the object. The radiation thermometer can accurately measure a surface temperature of the wafer in a case in which the film having a film thickness equal to or more than a certain degree is formed on the wafer, but is difficult to measure an accurate temperature of a thin film since a thin-film interference occurs. The thin-film interference means that the infrared light and visible light radiated from the surface of the thin film and the infrared light and visible light radiated from an underlying layer of the thin film interfere with each other.
Since an emissivity is varied when the thin-film interference occurs, it is possible to improve the accuracy in measurement of the temperature by correcting the temperature on the basis of the reflectivity and the emissivity of the incident infrared light. However, an emissivity correction thermometer which performs such temperature correction uses the reflectivity depending on the surface state, and, in fact, fails to obtain a sufficient accuracy regardless of the extremely high price. Thus, there is a demand for a method which is capable of growing a film with high quality without using the emissivity correction thermometer even in a state in which the thin-film interference occurs.